Jars, such as hydraulic jars, are used in downhole environments to provide impact force. Such tools are useful when a fishing or drilling string is stuck within a well bore and it is necessary to apply an impact force at the stuck location of the string to attempt to loosen it. Similarly, jars can be used in conjunction with fishing tools to provide the fishing tool with sufficient force for operation, for example, by providing an upward jarring force after the fishing tool has engaged a stuck tool.
Jars may be constructed to provide an impact force in either the “up,” or “upward” (toward the surface) or “down,” or “downward” (away from the surface) directions. Those of skill in the art will recognize that “up” and “down” are so defined because use of horizontal drilling techniques may result in situations in which “up” and “down” are not vertical. Similarly, as used herein, the “lower” portion of a tool or a part thereof is in the “downward” direction in respect to the “upper” portion. For maximum flexibility, ajar can be constructed to provide bidirectional impact, that is, it can fire (provide impact blows) in either the “up” or “down” directions at the choice of the operator on the surface.
However, in some applications, particularly those using coiled tubing, the length of the tools used is of great importance. With coiled tubing, it is greatly desirable to have shorter tools, because multiple tools must often be assembled in combination at the surface, and the coiled tubing operation does not allow for successive assembly of tools as the string is run into a pressured hole. Accordingly, it is sometimes desirable to use ajar which fires in only one direction, because the needed apparatus is shorter than one designed for bi-directional use.
Jars used in these applications operate by setting, or cocking, the jar, then applying an upward or downward force on the jar. These jars comprise a mandrel, which moves relative to the tool body and which bears the primary impact of the jar. Both the mandrel and the tool body generally have anvil surfaces which form the contact surfaces where the mandrel and the tool body meet. When the tool is released from the set position, the mandrel and the tool body move relative to each other at high speed, and the respective anvil surfaces strike with great force, thus producing the impact force of the jar. The relative direction of travel of the mandrel to the tool body is determined by whether the jar is fired up or down.
Although the operation of such tools provides large impact forces where needed, the result is also a large amount of stress on the jar and its various parts. Accordingly, repeated operations of these tools can result in rapid wear and the need to replace or repair the jar. Because reliability of operation is important, it is desirable that a jar be designed and constructed to accommodate repeated high stress. However, the tools are size-constrained by the standard sizes used for downhole operations and the need for limiting the length of the tool, especially in conjunction with coiled tubing operations. In current jars, these factors have limited the ability of the tool to withstand repeated operations without the need for repair or replacement.
Accordingly, it is a goal of the invention to provide a jar that is substantially shorter than current jars.
It is another goal of the invention to provide a jar with improved capability to withstand repeated operation cycles.
It is a further goal of the invention to provide a jar capable of improved impact force.